1. Technical Field
The present invention relates to a liquid crystal display device, to a method of manufacturing a liquid crystal display device, and to an electronic apparatus.
2. Related Art
In general, an electro-optical device, such as a liquid crystal display device, is used as a color image display unit of an electronic apparatus such as a cellular phone. In the liquid crystal display device, a liquid crystal layer is interposed between a pair of transparent substrates. In a method of manufacturing the liquid crystal display device, first, a sealing member is applied to a peripheral portion of one of the pair of substrates. At that time, an inlet for injecting liquid crystal is formed in a portion of the sealing member. Then, spacers are dispersed into the sealing member, and the two substrates Are bonded to each other with the sealing member interposed therebetween. In this way, a liquid crystal cell is formed in a region surrounded by the pair of substrates and the sealing member. Subsequently, the liquid crystal cell is de-aerated under a vacuum, and the atmosphere of the liquid crystal cell is changed from the vacuum state to an ambient pressure state while the inlet for injecting liquid crystal is dipped into a liquid crystal bath. As such, the liquid crystal flows into the liquid crystal cell by a difference in pressure between the liquid crystal cell and the outside and surface tension. Unfortunately, this method requires a long time to fill the liquid crystal into the liquid crystal cell. In particular, when a large substrate having a diagonal line of larger than 1 m is used, it takes one or more days to fill the liquid crystal.
Therefore, there has been proposed a method of discharging liquid crystal on a substrate provided with a frame-shaped sealing material not having a liquid crystal injecting port and of bonding substrates. In this method, first, a sealing material, such as thermosetting resin, is applied to a peripheral portion of the surface of one substrate. Then, a predetermined amount of liquid crystal is discharged inside the sealing material by a liquid discharging apparatus. Finally, the substrates are bonded to each other with the sealing material interposed therebetween under a vacuum, and the atmosphere of the substrates is changed from the vacuum state to the ambient pressure state. Then, ultraviolet rays are radiated onto the sealing material, or a heating treatment is performed thereon, thereby forming a liquid crystal display device. Thus, unlike the liquid crystal injecting method in the related art, the sealing material is formed in a ring shape without an injection port.
According to this method, after the two substrates are bonded to each other, an ambient pressure is applied to the substrates. Therefore, uniform pressure is applied to the two substrates, which makes it possible to obtain a predetermined cell gap. In addition, the cell gap can be determined by the discharge amount of liquid crystal. For example, when a very small amount of liquid crystal is discharged, a small cell gap is formed, which causes the occurrence of bubbles. On the other hand, when a very large amount of liquid crystal is discharged, a large cell gap is formed, which causes an irregularity of the cell gap. Therefore, it is possible to obtain a uniform cell gap by optimally setting the discharge amount of liquid crystal. In addition, unlike the liquid crystal injecting method according to the related art, this method makes it possible to reduce the amount of liquid crystal used and thus to shorten the time required for an injecting/sealing process, resulting in a short tact-time.
Further, a sealing member forming method using a dispenser has been proposed (for example, JP-A-2002-98979, JP-A-2003-222883, and JP-A-2003-241204). In this method, a sealing member is formed in a predetermined pattern on a substrate while moving the dispenser relative to the substrate. Here, for the sealing member discharged on the substrate to have a ring-shaped pattern, a sealing member previously discharged in a part of a peripheral portion of the pattern overlaps a sealing member discharged later. In this way, when the substrates are bonded to each other after the liquid crystal is discharged, it is possible to prevent the liquid crystal from leaking to the outside of the ring-shaped pattern of the sealing member.
However, the inventors found out that the liquid crystal display device disclosed in the related art had the following problems: it is difficult to stably form the sealing member; it is necessary to form dummy spacers between adjacent panels; and it is necessary to control the dispenser when a sealing member forming process starts and ends in order to form one pattern in one forming operation. In addition, the inventors found out that a general method of forming a sealing member using a dispenser had a problem in that the irregularity of a cell gap easily occurs.
The inventors obtain the following knowledge from the sealing member discharging method using the dispenser.
In the above-mentioned discharging method, as shown in FIGS. 26A and 26B, it is necessary that a sealing member forming start portion 500 and a sealing member forming end portion 510 be formed to have the same thickness as those of the other portions. The reason is that, when the thicknesses thereof are excessively large, a large cell gap is formed, resulting in display irregularity, and when the thicknesses thereof are excessively small, liquid crystal is leaked from those portions, resulting in low reliability. Therefore, when the sealing member is formed by the dispenser, generally, the sealing member may be formed to be large or small by the sealing member forming start portion 500 and the sealing member forming end portion 510, as shown in FIGS. 26A and 26B. Therefore, as shown in FIG. 26C, in order to make the thickness of a connecting portion 520 uniform, the sealing member forming start portion 500 generally overlaps the sealing member forming end portion 510. In this case, it is confirmed that the overlapping portion needs to have a length of about 4 mm, and a width W2 of the overlapping portion becomes larger than a predetermined width W1 by about 0.1 to 0.2 mm (ΔW=W2−W1=0.1 to 0.2 mm) due to a variation in the viscosity of the sealing member.
Further, in a liquid crystal display device driven by TFDs (thin film diodes) or a liquid crystal display device in which STN (super twisted nematic) liquid crystal is operated by a passive driving method, as shown in FIGS. 27 and 28, it is necessary that lead wiring lines 601 formed on the surface of a circuit board having driver ICs 600 and 610 thereon and common electrodes (hereinafter, referred to as COM electrodes) 602 formed on a counter substrate be electrically connected to connection pads 603. In this case, conductive particles, spacers, on which a coating process is performed, are dispersed into a sealing member, and the sealing member is arranged on the connection pads 603. In this way, the lead wiring lines 601 and the COM electrodes 602 are electrically connected to each other through the conductive particles, so that an output voltage from the driver ICs 600 is applied to wiring lines on the counter substrate.
Meanwhile, it is necessary that the sealing member be formed to cross segment electrodes (hereinafter, referred to as SEG electrodes) 604 extending from the driver IC 610 to a display area 620 and the lead wiring lines 601 extending from the driver ICs 600 to the connection pads 603. In this case, in order to prevent the lead wiring lines 601 and the SEG electrodes 604 from being electrically connected to each other, a sealing member not containing conductive particles crosses the lead wiring lines 601 and the SEG electrodes 604.
When both the sealing member containing the conductive particles and the sealing member containing the non-conductive particles are used, it is necessary that the two sealing members be connected to each other between an end of the connection pad 603 (which is represented by a character ‘A’ in FIG. 28) and a portion where the COM electrode 601 crosses the sealing member (which is represented by a character ‘B’ in FIG. 28). In the liquid crystal display device using the TFDs or the STN liquid crystal display device, generally, a distance L between the two portions is smaller than 2 mm. Therefore, when the distance is smaller than the length of the overlapping portion, 4 mm, shown in FIG. 26C, it is confirmed that the overlapping portion of the connecting portion 520 has a length of 1 mm, and a width W3 of the overlapping portion is larger than the predetermined width W1 by about 0.5 to 0.6 mm (ΔW=W3−W1=0.5 to 0.6 mm), which causes the irregularity of a cell gap.
In the method disclosed in JP-A-2002-98979, the width of an overlapping portion of a start portion and an end portion of a sealing line is 0.4 to 0.6 times the width of the sealing line. However, in this method, it is very difficult to control a dispenser, and thus it takes a long time to form the sealing member. In addition, the shape of the sealing member may be varied due to a variation in the amount of the sealing member remaining in the dispenser or a variation in viscosity between the lots of the sealing member, which causes trouble in managing the dispenser.
Further, in the method disclosed in JP-A-2003-222883, the formation of a sealing member starts from any portion at the outside of the sealing member having a closed loop shape, and the formation thereof is terminated in another portion at the outside of the sealing member having the closed loop shape, which is different from the sealing member formation start portion. However, this method has a problem in that dummy spacers should be provided between adjacent panels. In addition, in JP-A-2002-98979, JP-A-2003-222883, and JP-A-2003-241204, since only one member is formed by one sealing member forming operation, it takes a long time to control the dispenser when the formation of the sealing member starts or is terminated, which results in a long tact time.